Method for fabricating a copper alloy and copper alloy fabricated by the same

ABSTRACT

A method for fabricating a copper alloy. Cu and Cr, Zr, and Sn to be doped to the Cu are melt to cast a copper alloy material. Hot working is carried out on the copper alloy material to form a plate material having a rolled texture. Heat treatment is carried out on the plate material. Cold rolling with workability of 80% or more and less than 90% is carried out on the plate material after the heat treatment to form an intermediate plate material. Aging treatment is carried out on the intermediate plate material. Another cold rolling with workability of 20% to 40% is carried out as finish rolling on the intermediate plate material after the aging treatment step. The intermediate plate material after the finish rolling step is heated as stress relief annealing.

The present application is based on Japanese Patent Application No. 2009-144937 filed on Jun. 18, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating a copper alloy and a copper alloy fabricated by the same, in more particular, to a method for fabricating a copper alloy to be used for electric parts and electronic components and the copper alloy fabricated by this method.

2. Related Art

Various characteristics are required for materials to be used for electric parts and electronic components such as connector, relay, switch, lead frame, lithium ion battery. As a spring material, sufficient strength for obtaining a high contact pressure, anti-stress relaxation property (stress relaxation resistance) for maintaining the contact pressure even after the use for a long period at a high temperature, high electric conductivity for suppressing generation of Joule heat in energization and dissipating the generated heat, and sufficient bending characteristic for realizing a complex bending work without generating any cracks or the like are required.

In recent years, the parts or components used for various electric and/or electronic devices have been miniaturized in accordance with miniaturization, reduction in thickness, and lightweighting of the various electric and/or electronic devices. Current density in electrodes or the like used in the various parts is increased compared with conventional devices, as a result of the miniaturization of such a part. Therefore, a demand for using the materials with excellent electric conductivity compared with the conventional materials is increased. Further, since the parts for on-vehicle purpose are demanded to have durability in use in an environment with higher temperature, a demand for the material with high anti-stress relaxation property is increased. As the material satisfying the demand of the high electric conductivity and the anti-stress relaxation property, a Cu—Cr—Zr based alloy and the like have been proposed.

For example, Japanese Patent Laid-Open No. 7-258805 (JP-A 7-258805) discloses a conventional method for fabricating a Cu—Cr—Zr based alloy material comprising steps of preparing a copper alloy comprising Cr of 0.05 to 0.40%, Zr of 0.03 to 0.25%, Fe of 0.10 to 1.80%, Ti of 0.10 to 1.80%, a Fe/Ti weight ratio being 0.66 to 2.6 in range of 0.10%≦Ti≦0.60%, the Fe/Ti weight ratio being 1.1 to 2.6 in range of 0.60%<Ti ≦0.80%, and a balance being Cu and inevitable impurities, successively carrying out solution treatment at a temperature less than 950° C., cold working at workability of 50 to 90%, aging treatment at a temperature of 300 to 580° C., cold working at workability of 16 to 83%, and heat treatment at a temperature of 350 to 700° C. for annealing on the copper alloy in this order.

The conventional method for fabricating a copper alloy disclosed by JP-A 7-258805 provides a copper alloy which is excellent in various characteristics such as tensile strength, elongation, electric conductivity.

However, there are following disadvantages in the method of fabricating a copper alloy disclosed by JP-A 7-258805. Namely, since the solution treatment at the high temperature is carried out, metal texture of a parent phase may be coarsened. The coarsening of the metal texture may partially soften the copper alloy, and cause deterioration of the bending characteristic.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a method for fabricating a copper alloy with high strength and good bending characteristic with maintaining electric conductivity and anti-stress relaxation property of the Cu—Cr—Zr based copper alloy, and a copper alloy fabricated by the same.

According to a feature of the invention, a method for fabricating a copper alloy comprises:

melting step of melting Cu and Cr, Zr, and Sn to be doped to the Cu to cast a copper alloy material;

hot working step of carrying out a hot working on the copper alloy material to form a plate material having a rolled texture;

heat treatment step of carrying out a heat treatment on the plate material;

intermediate rolling step of carrying out a cold rolling with a workability of 80% more and less than 90% on the plate material after the heat treatment step to form an intermediate plate material;

aging treatment step of carrying out an aging treatment on the intermediate plate material;

finish rolling step of carrying out another cold rolling with a workability of 20% to 40% on the intermediate plate material after the aging treatment step; and

stress relief annealing step of carrying out a heating on the intermediate plate material after the finish rolling step.

The heat treatment step may comprise carrying out the heat treatment at such a temperature that the rolled texture is reduced by generating recrystallization in the rolled texture while suppressing coarsening of a grain size of crystal in the plate material.

The heat treatment step may comprise carrying out the heat treatment at such a temperature that a grain size of a copper alloy crystal contained in the copper alloy is 50 μm or less.

The temperature of the heat treatment is preferably 700° C. or more and less than 950° C.

The aging treatment step may comprise carrying out the aging treatment at a temperature of 390° C. to 450° C. on the intermediate plate material.

The stress relief annealing step may comprise carrying out the heating at a temperature of 400° C. to 600° C. on the intermediate plate material.

The melting step preferably comprises casting the copper alloy material comprising the Cr of 0.1 to 0.4% by weight, the Zr of 0.02 to 0.2% by weight, and the Sn of 0.01 to 0.3% by weight.

The method may further comprise:

rough rolling step of carrying out a further cold rolling on the plate material,

wherein the heat treatment step comprises carrying out the heat treatment on the plate material after the rough rolling step.

The heat treatment step may comprise carrying out the heat treatment at such a temperature that a grain size of a copper alloy crystal contained in the copper alloy is 30 μm or less.

The temperature of the heat treatment is preferably 700° C. or more and less than 850° C.

According to another feature of the invention, a copper alloy may comprise:

Cr of 0.1 to 0.4% by weight, the Zr of 0.02 to 0.2% by weight, and the Sn of 0.01 to 0.3% by weight, a balance being Cu and inevitable impurities.

The copper alloy preferably has an electric conductivity of 80% IACS or more and a strength of 550 MPa or more.

ADVANTAGES OF THE INVENTION

According to the present invention, it is possible to provide a method for fabricating a copper alloy with high strength and good bending characteristic while maintaining electric conductivity and anti-stress relaxation property of the Cu—Cr—Zr based copper alloy, and the copper alloy fabricated by the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing a manufacturing process of a copper alloy in a preferred embodiment according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Next, an embodiment according to the present invention will be explained in more detail in conjunction with appended drawings.

Embodiment Copper Alloy

A copper alloy in this embodiment is a copper alloy used for electric parts and electronic components e.g. connector.

More concretely, the copper alloy material comprises Cr of 0.1 to 0.4% by weight, Zr of 0.02 to 0.2% by weight, and Sn of 0.01 to 0.3% by weight, and the balance being Cu and inevitable impurities.

Cr has a function for improving strength and heat resistance of the copper alloy, when Cr exists alone in a precipitated state in the parent phase of the copper alloy. Zr generates a compound with Cu. This compound has a function for improving the strength and heat resistance of the copper alloy, when Zr exists in a precipitated state in the parent phase of the copper alloy. Furthermore, Sn has a function for improving the strength of the copper alloy. Therefore, the strength of the copper alloy can be improved by doping Sn together with Cr and Zr to the Cu.

The copper alloy in the embodiment has electric conductivity of 80% IACS or more and strength of 550 MPa or more.

(Manufacturing Process for Fabricating the Copper Alloy)

FIG. 1 is a flow chart showing a manufacturing process of a copper alloy in this embodiment according to the present invention.

At first, Cu (copper), a predetermined amount of Cr, a predetermined amount of Zr, and a predetermined amount of Sn to be doped to the copper are melt in a low frequency fusion furnace, and a copper alloy material is cast as an ingot (Melting process: Step 10, and a “Step” will be abbreviated as “S” hereinafter). More concretely, in the melting process, a copper alloy material containing 0.1 to 0.4% by weight, Zr of 0.02 to 0.2% by weight, and Sn of 0.01 to 0.3% by weight is cast. Herein, oxygen free copper may be used as copper for the base material.

Next, a hot working (e.g. hot rolling) is carried out on the ingot at a temperature of about 900° C. to manufacture a copper alloy plate having a rolled texture (Hot working process: S20). Herein, the hot working process at the step S20 has a function of solution treatment for providing solid-solution of Cr and Zr precipitates within the ingot obtained by the melting process into the parent phase once. According to the solution treatment function of the hot working process, it is possible to homogenize a distribution state of the Cr and Zr precipitates generated at an aging treatment process (to be described later) in the copper alloy, and provide the Cr and Zr precipitates with fine texture.

Successively, the copper alloy plate is cold rolled (Rough rolling process: S30). Next, annealing is carried out as heat treatment on the cold rolled plate (Heat treatment process: S40). The heat treatment process includes steps of carrying out a heat treatment at such a temperature that the rolled texture is reduced by generating recrystallization in the rolled texture while suppressing coarsening of a grain size of crystal in the plate, and quenching the plate after the heat treatment. More concretely, the heat treatment process includes a step of carrying out such a heat treatment that the grain size of copper alloy crystal contained in the copper alloy is 50 μm or less, more preferably 30 μm or less on the plate, and a step of quenching the heat treated plate. Herein, the value of the grain size is the value after quenching the plate after the heat treatment. Distortion generated in the hot working process can be canceled by the heat treatment at the heat treatment process, thereby improving the bending characteristic.

In addition, it is possible to provide the grain size in the copper alloy with the fine texture, thereby improving the strength of the fabricated copper alloy by carrying out the heat treatment process. Herein, the heat treatment at the heat treatment process is carried out within a temperature range of 700° C. or more and less than 950° C., preferably within a temperature range of 700° C. or more and less than 850° C. The recrystallization is generated by carrying out the heat treatment within the above temperature ranges, so that the rolled texture generated by the hot working process disappears as described above. As a result, it is possible to provide the crystal of the copper alloy with the grain size 50 μm or less (namely, within a temperature range of 700° C. or more and less than 950° C.), more preferably 30 μm or less (namely, within a temperature range of 700° C. or more and less than 850° C.). According to this process, even when the bending work is carried out on the produced copper alloy, it is possible to suppress surface roughening at a bent section.

Successively, another cold rolling process with workability of 80% or more and less than 90% is carried out on the copper alloy plate after the heat treatment to form an intermediate copper alloy plate (Intermediate cold rolling process: S50). Furthermore, aging treatment is carried out at a temperature of 390 to 450° C. for a predetermined time on the intermediate copper alloy plate passed through the intermediate cold rolling process, and the intermediate copper alloy plate is slowly cooled (Aging treatment process: S60). According to these processes, work hardening can be combined with precipitation hardening, so that it is possible to improve the characteristics such as strength, electric conductivity of the produced copper alloy. Herein, the intermediate plate is work-hardened by controlling the workability to be greater than 80% in the intermediate rolling process, thereby improving the strength of the intermediate plate. In addition, a lot of lattice defects (dislocations) are introduced into the intermediate plate by the cold rolling in the intermediate rolling process. Since the lattice defect functions as an origin of the precipitation of precipitates (e.g. compound of Cr and Cu, compound of Zr and Cu) having a size of around several nanometers in the precipitation hardening in the aging treatment process, the aging treatment process has a function of promoting uniform dispersion of the precipitates (e.g. compound of Cr and Cu, compound of Zr and Cu) in the intermediate plate.

In addition, although ductility of the intermediate plate falls in the cold working in the intermediate rolling process, it is possible to restitute the ductility that has fallen by the aging treatment process. Herein, the aging treatment is carried out at a temperature of 390° C. or more for the purpose of making the fine precipitates precipitate in the intermediate plate enough. In addition, the aging treatment is carried out at the temperature of 450° C. or less for the purpose of controlling degradation of the strength due to softening of the intermediate plate. In the aging treatment process, the precipitates are precipitated in the intermediate plate while keeping the intermediate plate at a predetermined temperature. The strength and electric conductivity of the produced copper alloy can be improved by the fine precipitates precipitated in the intermediate plate in the aging treatment process.

Next, a still another cold rolling with workability of 20% to 40% is carried out on the intermediate plate to which the aging treatment was carried out (Finish rolling process: S70). The finish rolling process is carried out with the workability of 20% or more, by which enough work hardening is obtained for the purpose of providing the copper alloy with enough strength. In addition, the finish rolling process is carried out with workability of 40% or less for the purpose of controlling the degradation of the conductivity, the degradation of the ductility and the degradation of bending characteristic of the produced copper alloy. By the finish rolling process, the intermediate plate on which the aging treatment was carried out is work-hardened, so that the strength can be improved.

Successively, the heat treatment of temperature of 400° C. to 600° C. is carried out for short time (e.g. about 1 minute) on the intermediate plate on which the cold rolling was carried out (Stress relief annealing process: S80). In the stress relief annealing process, heat treatment at a temperature of 400° C. or more is carried out for the purpose of providing the produced copper alloy with enough spring characteristic and ductility. Further, in the stress relief annealing process, heat treatment at a temperature of 600° C. or less is carried out for the purpose of preventing degradation of the strength of the produced copper alloy due to re-solution of the precipitates to the copper alloy. According to the stress relief annealing process, it is possible to obtain the copper alloy in this embodiment, which has the improved spring characteristic, and the ductility of the copper alloy which have fallen once due the finish rolling process is restituted. By carrying out the respective processes described above, the copper alloy in this embodiment is fabricated.

Effect of this Embodiment

The copper alloy in this embodiment of the present invention is fabricated by carrying out the respective processes, and the rolled texture disappears by the heat treatment at the temperature of 700° C. or more and less than 950° C., so that the copper alloy has the crystal structure with the crystal grain size of 50 μm or less. Therefore, the copper alloy is excellent in the electric conductivity, strength, bending characteristic, and stress relaxation resistance, in addition, the balance thereof is excellent. Accordingly, it is possible to provide the copper alloy contributing to the downsizing and high integration of electric/electronic components.

Examples

Copper alloy according to Examples 1 to 3 that were fabricated based on the embodiment of the present invention and copper alloy according to Comparative examples 1 to 4 will be explained below.

TABLE 1 shows treatment conditions of the copper alloys in the heat treatment process and respective characteristics of the produced copper alloys according to the Examples 1 to 3 and the Comparative examples 1 to 2. TABLE 2 shows treatment conditions of the copper alloys in the intermediate rolling process and respective characteristics of the produced copper alloys according to the Example 1 and the Comparative examples 3 to 4.

TABLE 1 Heat Treatment Metal texture after Specific temperature in the the heat treatment electric Tensile heat treatment Presence of Average grain conductivity Strength Elongation MBR/t process (° C.) rolled texture size (μm) (% IACS) (MPa) (%) (*) Example 1 700 No 10 82 560 9 0 Example 2 800 No 20 83 558 8 0 Example 3 900 No 50 82 550 5 0 Comparative 600 Yes — 86 527 8 0.4 Example 1 Comparative 1000 No 300  79 550 4 0.6 Example 2 (*) MBR: Minimum Bending Radius, t: plate thickness

TABLE 2 Working condition Specific Workability in Workability electric Tensile the intermediate in the finish conductivity Strength Elongation rolling process (%) rolling process (%) (% IACS) (MPa) (%) MBR/t Example 1 83 40 82 560 9 0 Comparative 95 40 83 543 6 0.4 example 3 Comparative 0 97 45 530 6 0.6 example 4

Example 1

At first, a copper alloy comprising oxygen free copper as a base material, 0.25% by weight of Cr, 0.1% by weight of Zr, and 0.15% by weight of Sn was melt in a low frequency fusion furnace, and the copper alloy material was cast to be an ingot (Melting process). Next, hot working was carried out on the ingot to have a thickness of 8 mm (Hot working process). Successively, the copper alloy plate was cold rolled to have a thickness of 2.5 mm (Rough rolling process). Next, heat treatment at a temperature of 700° C. was carried out on the cold rolled alloy material for annealing (Heat treatment process). Successively, another cold rolling process with workability of 83% was carried out (Intermediate rolling process). Furthermore, aging treatment was carried out at a temperature of 430° C. for 2 hours (Aging treatment process). After the aging treatment process, a still another cold rolling with workability of 40% was carried out (Finish rolling process). Successively, the heat treatment of temperature of 450° C. was carried out for 60 seconds (Stress relief annealing process) to fabricate the copper alloy according to Example 1.

Materials having the same composition as that of Example 1 were melt and cast, and only heat treatment condition in the heat treatment process was changed. After carrying out the processes similar to those of Example 1, copper alloys according to Examples 2 to 3 and Comparative examples 1 to 2 were fabricated.

Further, materials having the same composition as that of Example 1 were melt and cast, and only workability in the intermediate rolling process and workability in the finish rolling process were changed. After carrying out the processes similar to those of Example 1, copper alloys according to Comparative examples 3 to 4 were fabricated.

A part of the copper alloy just after stress relief annealing was sampled as a test piece for each of the copper alloys in Examples 1 to 3 and Comparative examples 1 to 2. A surface of a cross section perpendicular to a rolling direction of the test piece was polished and etched. By using the test piece obtained as above, presence of rolled texture was observed. For the test piece, in which no rolled texture was observed, an average value of crystal grain sizes in a plate thickness direction was calculated to provide an average crystal grain size.

Further, a tensile test was carried out on the copper alloys according to Examples 1 to 3 and Comparative examples 1 to 4. The tensile test was carried out in accordance with JIS Z 2201, and tensile strength and elongation in a direction parallel with the rolling direction were measured. Still further, in accordance with JIS H 3130, W-bending test in Bad-Way (i.e. a bending axis is in a direction same as the rolling direction) was carried out, and MBR/t value that is a ratio of a minimum bending radius (MBR) for no-crack state to a plate thickness (t) was calculated. Results of each characteristic are shown in TABLE 1 and TABLE 2.

Referring to TABLE 1 and TABLE 2, the copper alloys according to Examples 1 to 3 have the electric conductivity of 82% IACS or more, and high strength of about 550 MPa. Further, the copper alloys according to Examples 1 to 3, no crack occurred by the W-bending test, namely, the good bending characteristic was shown. Therefore, the copper alloy according to the present invention may be used as a copper alloy for a connector or a copper foil for lithium ion battery which requires excellent bending characteristic, and may be used as a copper alloy for a lead frame which requires a high electric conductivity.

On the other hand, the copper alloy according to Comparative example 1 is the copper alloy that was fabricated by the heat treatment process at a temperature lower than the heat treatment condition of the heat treatment process in Examples 1 to 3. As to the copper alloy according to Comparative example 1, it was observed that the rolled texture remained inside and it was shown that enough bending characteristic was not provided due to the work distortion increased by the cold rolling. In addition, the copper alloy according to Comparative example 2 is the copper alloy that was fabricated by the heat treatment process at a temperature higher than the heat treatment condition of the heat treatment process in Examples 1 to 3. As to the copper alloy according to Comparative example 2, it was observed that the average grain size after the heat treatment was coarsened and it was shown that enough tensile strength and bending characteristic were not provided.

The copper alloy according to Comparative example 3 is the copper alloy that was fabricated with the workability in the cold rolling process before the aging treatment is greater than the workability for fabricating the copper alloys according to Examples 1 to 3. As to the copper alloy according to Comparative example 3, it was shown that the tensile strength was small and the bending characteristics was not good.

The copper alloy according to Comparative example 4 is the copper alloy that was fabricated with the workability in the cold rolling process before the aging treatment is smaller than the workability for fabricating the copper alloys according to Examples 1 to 3. As to the copper alloy according to Comparative example 4, effect of the aging treatment was not enough, due to insufficient introduction of dislocation by the cold rolling process before the aging treatment. It was shown that the electric conductivity and tensile strength were small, and the bending characteristic was not good.

Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be therefore limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. 

1. A method for fabricating a copper alloy comprising: melting step of melting Cu and Cr, Zr, and Sn to be doped to the Cu to cast a copper alloy material; hot working step of carrying out a hot working on the copper alloy material to form a plate material having a rolled texture; heat treatment step of carrying out a heat treatment on the plate material; intermediate rolling step of carrying out a cold rolling with a workability of 80% more and less than 90% on the plate material after the heat treatment step to form an intermediate plate material; aging treatment step of carrying out an aging treatment on the intermediate plate material; finish rolling step of carrying out another cold rolling with a workability of 20% to 40% on the intermediate plate material after the aging treatment step; and stress relief annealing step of carrying out a heating on the intermediate plate material after the finish rolling step.
 2. The method for fabricating a copper alloy according to claim 1, wherein the heat treatment step comprises carrying out the heat treatment at such a temperature that the rolled texture is reduced by generating recrystallization in the rolled texture while suppressing coarsening of a grain size of crystal in the plate material.
 3. The method for fabricating a copper alloy, according to claim 2, wherein the heat treatment step comprises carrying out the heat treatment at such a temperature that a grain size of a copper alloy crystal contained in the copper alloy is 50 μm or less.
 4. The method for fabricating a copper alloy, according to claim 3, wherein the temperature of the heat treatment is 700° C. or more and less than 950° C.
 5. The method for fabricating a copper alloy, according to claim 1, wherein the aging treatment step comprises carrying out the aging treatment at a temperature of 390° C. to 450° C. on the intermediate plate material.
 6. The method for fabricating a copper alloy, according to claim 1, wherein the stress relief annealing step comprises carrying out the heating at a temperature of 400° C. to 600° C. on the intermediate plate material.
 7. The method for fabricating a copper alloy according to claim 1, wherein the melting step comprises casting the copper alloy material comprising the Cr of 0.1 to 0.4% by weight, the Zr of 0.02 to 0.2% by weight, and the Sn of 0.01 to 0.3% by weight.
 8. The method for fabricating a copper alloy, according to claim 1, further comprising: rough rolling step of carrying out a further cold rolling on the plate material, wherein the heat treatment step comprises carrying out the heat treatment on the plate material after the rough rolling step.
 9. The method for fabricating a copper alloy, according to claim 2, wherein the heat treatment step comprises carrying out the heat treatment at such a temperature that a grain size of a copper alloy crystal contained in the copper alloy is 30 μm or less.
 10. The method for fabricating a copper alloy, according to claim 9, wherein the temperature of the heat treatment is 700° C. or more and less than 850° C.
 11. A copper alloy comprising: Cr of 0.1 to 0.4% by weight, the Zr of 0.02 to 0.2% by weight, and the Sn of 0.01 to 0.3% by weight, a balance being Cu and inevitable impurities.
 12. The copper alloy, according to claim 11, wherein the copper alloy has an electric conductivity of 80% IACS or more and a strength of 550 MPa or more. 